Motor control



J. A SHEPARD MOTOR CONTROL A ril 20, 1937.

2 Sheets-Sheet 1 Filed Feb. 15, 1933 INVENTOR. 6/ v fil ffj 6 5/15/ 480 April 1937- J. A. SHEPARD 2,077,904

MOTOR CONTROL Filed Feb. 15, 1933 2 Sheets-Sheet 2 F02 wmea I N V EN TOR, Jq/vas ,4. Slu /MRO.

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A TTORNEY Patented Apr. 20, 1937 UNITED STATES PATENT QFFECE MOTOR CONTROL York Application February 15, 1933, Serial No. 656,828

7 Claims.

The general object of the present invention is to provide a master switch mechanism which is characterized by its light weight, compactness, and easy and efficient operation, and which is adapted to separately energize and de-energize the electro-magnetic switches employed to regulate the current supply to, and speed of, an electric motor or, of an associated plurality of electric motors with each of which a plurality of said 10 electro-magnetic switches is combined.

My present invention was primarily devised and is especially adapted for use in a hoisting mechanism such as a hoist or crane operated from the floor by means of a pendent control device.

Prior to my invention the only available means has been either pendent ropes, one for the hoisting motion and another for the reverse, or lower. ing motion, or else with a pendent push button station suspended from the hoist or crane by a flexible cable comprising the necessary motor operating conductors, and carrying two buttons, one for the hoisting motion and one for the reverse, or lowering motion.

The former is applicable to either single speed, or variable speed and has been heretofore invariably employed where variable speed of the motor was essential, but is subject to the objection that in changing from one motion to the other, the attention of the operator is distracted from the work being performed in order to locate the other swinging rope. Where two or more motors are to be controlled the multiplicity of pendent swinging ropes is confusing to the operator, and, hence, through error, may cause serious accident from pulling the wrong rope.

Where bulky loads are handled the operator may not be able to stand directly under the control equipment and thus may be unable to reach the ropes for alternative motions. Also serious accidents have been occasioned by moving loads catching one of the pendent ropes and starting a motion not intended by the operator.

The latter or pendent push button station method has been subject tothe objection that a single on position only is obtainable without any measure of speed control, other than the objectionable expedient of alternately energizing and de-energizing the motor with such frequency as to prevent the motor from attaining its full speed during the periods in which it is energized. Also since single speed operation is practicable for small motors only, the last mentioned method has been seriously limited in its scope. This method has, however, the advantage that the push button station for a number of motors can be carried in one hand andall motions reliably selected without distracting the attention of the operator from his other duties.

My invention adds to the advantages of pendent push button operation the ability to secure speed control, either varying upward, downward, or continuously on any selected step. The extreme compactness and lightness of the push button permits its being conveniently carried by the operator in his various movements, released or grasped instantly, as the exigencies of his work may require.

Through that feature of my invention which introduces small relay electro-magnetic switches, directly operated by the push button, which in turn closes the circuit to the magnet coils of larger electro-magnetic switches, the scope of push button control is increaed from only a few H. P. to the largest motors employed in industry; the primary unit, the push button, being no larger or heavier for 1000 H. P. than for 1 H. P., hence by the present invention I am able to obtain the advantages of speed control heretofore obtainable only with a heavy and bulky stationary master switch mechanism.

The energy delivered by the spring return movement of a push button is necessarily limited to avoid fatigue of the operator in holding it to the on position, hence the entrance of foreign matter from the hands of workmen is always a present danger with the consequent failure of the push button to return to the off position when desired. I therefore, provide an emergency stop which is advantageously in the form of a switch mounted in the switch button control mechanism, and which is adapted to open the circuit of all push buttons and therefore bring all motions to rest until repairs can be made.

In the preferred mode of accomplishing the object of the present invention, I employ a master switch mechanism comprising a plurality of push button switch units characterized by their inherent light weight and compactness, and by the ease and reliability with which each may be adjusted into one or another of a plurality of different on positions.

Specific objects of the present invention are to provide a push button switch mechanism having a plurality of diiferent on positions and characterized by the provisions for obtaining a relatively long travel of the push button proper and the successive engagement of the latter by a plurality of contacts during such travel with a suitable contact pressure, all without sacrifice of desirable compactness and economy in weight,

and without taxing the finger strength of the operator and without making it difficult for the latter to place the push button in, and maintain it in any particular on position.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its advantages and specific objects attained with it, reference should be had to the accompanying drawings and descriptive matter, in which I have illustrated and described a preferred embodiment of the invention.

Of the drawings:

Fig. 1 is an elevation of a portion of a master switch mechanism comprising a plurality of switch button units;

Fig. 2 is an elevation partly broken away and in section of one of the push button units shown in Fig. 1;

Fig. 3 is a bottom or inverted plan view of the switch unit shown in Fig. 2;

Fig. 4 is an elevation taken at right angles to Fig. 2;

Fig. 5 is a section on the line 5-5 of Fig. 4;

Fig. 6 is a diagram of a motor control system including two push button switch units of the type shown in Figs. 1-5; and

Fig. 7 is a diagram of a portion of a motor control system of modified form.

The push button master switch shown in Fig. 1 comprises a housing or casing M composed of separable side parts normally connected by transverse screws M. Mounted within the housing M are a plurality of similar push button switch units, each of which comprises a body or frame portion A having a reduced neck portion A extending through an aperture M in one of the side members of the casing M. The latter is formed at one end with a neck or collar M surrounding the cable N by which the casing may be suspended from an overhead portion of an electric crane or hoist mechanism and which may comprise the motor control conductors through which the push button switch units control the different motors of said crane or hoist mechanism.

The push button switch units may be, and are shown as of identical construction, so that a description of one will suflice for all.

The body member A of each push button switch is preferably formed of some mechanically strong insulating material as bakelite. As shown, the body A is rectangular in cross sectional outline and is formed with a central cylindrical chamber A communicating at its outer end with an opening A of smaller diameter, in the end portion A of the body A. Extending into the chamber A of each body A through its opening A is a push button or switch actuating member B formed of some suitable strong insulating material and of an external diameter to have an easy sliding fit in the opening A The end of the push button B inserted within the chamber A is surrounded by a ferrule or thimble b of copper or other good conducting metal. The external diameter of the thimble b is greater than the diameter of the opening A and in the oil position of the switch, the outer end of the thimble or sleeve b engages the end wall of the chamber A at the margin of the opening A The push button member B is biased to its off position by a return spring C. The latter is coaxial with the push button B and has its outer end received in a central socket B in the member B, extending from the inner end of the latter nearly to its outer end. The inner end of the spring C surrounds a guide post d centrally disposed in the chamber A and anchored at its lower end in a plug or block of insulating material D normally closing the inner end of the chamber A As shown, the post d is provided with a collar d adapted to bear against the side of the casing M adjacent the block D, and said casing side is formed with apertures M for receiving and positioning the short portions of the posts d projecting from the adjacent sides of the collars d of the difierent push button switch units. The post (1 is of a length to extend some distance into the cavity B when the push button B is in its off or outer position. The return spring C acts between the block D and the closed end of the cavity B and surrounds the post d. The described arrangement permits of the use of a relatively long return spring C so that the tension of the latter need not be objectionably increased when the push button is given its maximum movement inward from its outer or off position.

As the push button is moved inward through it full range of movements, its conducting thimble or sleeve b successively engages contacts located at progressively increasing distances from the outer end of the chamber A. As shown, there are six such contacts, E, E E E E and E which are similarly spaced apart longitudinally of the push button. Each of said contacts is in the form of a ball of bronze or other suitable material, and is located in a corresponding radial opening A in the wall portion of the member A surrounding the chamber A Each of the contacts E, E E E, E and E is mounted in a corresponding resilient contact support F, F F F F and F respectively. Each of said cont-act supports subjects the contact which it supports to a yielding force which tends to hold the latter in a position in which it extends into the path of movement of the thimble b and insures the desired contact pressure when the thimble engages the contact.

To reduce the resistance to the movement of the push button due to its engagement with the contacts, each of the latter is so supported as to permit it to rotate about an axis parallel to the tangent to the thimble b at the point of its engagement of the contact and thimble. To this end, each contact is formed with an axial passage through which a portion of the corresponding contact support loosely passes. effects of the side thrust on the push button of the different contacts engaged by the push button sleeve or thimble b, the contacts are arranged in two diametrically opposed sets, one set including the contacts E, E and E and the other set including the contacts E E and E In the construction illustrated, each of the contact supports F, F F etc., is in the form of an elongated piece of spring wire generally of L-shape, and, with the long end of the L terminating in a portion F bent about screws H and H for anchoring that end of the contact support to the body A. As shown, the screws H and H for the contact supports F, F and F are tapped into one, and the screws H and H b for the contact supports F F and F are tapped into the other of the two outer side walls of the body A which are transverse to the walls of the body containing the radial openings A The portion of each contact support extending paral- To minimize the lel to the side of the body A in which the corresponding contact is located, is received in a groove A When any contact E, E etc., is out of engagement with the thimble b its support F, F etc., engages the bottom of the corresponding groove A and the depth of the latter is such that the said contact is then held in a position in which it projects slightly into the path of movement of the thimble. As shown, the body A is formed with lugs or projections H extending at opposite sides of each screw H. Each of the screws H forms a means for connecting a terminal or motor control conductor I, 2, 3, etc., to the corresponding contact support F, F F etc. as is clearly shown in the drawings, the portions of the contact supports F, W, and F and F F and F which are at the same side of the body A as the corresponding screws H, are not parallel to one another, but are disposed to permit the screws H to be more widely spaced than are the corresponding contacts E, E etc. This is advantageous in that it permits of a relatively close spacing in the longitudinal direction of the chamber A of the contacts E, E etc., which is desirable in that it shortens the required length of the plunger and its operating stroke, while at the same time it permits the different screws H to be spaced more widely apart in the direction of the length of said chamber as is desirable to provide proper clearance between the connections of the different terminal conductors to the resilient contact supports effected by the different terminal connector screws H.

In operation, as each push button is moved inward from its off position, the end of the thimble b successively engages and cams outward the different contacts E, E E etc. Each of the latter, as the push button motion continues, rolls onto the periphery of the thimble b. The latter thus serves to electrically connect the contact E to each of the other contacts E E etc., which are in engagement with the thimble, in any particular position of the latter. The thimble b formed with a circumferential groove 12 which is entered by the contact E when the thimble b is in the first on position in which the thimble b connects the contacts E, and E and which is entered successively by the contacts E E, E and E as the thimble is successively advanced through its other intermediate positions and into its final on position. As each of the contacts E, E E E and E enters and leaves the groove b in the thimble b, the force, due primarily to the return spring C, which opposes the movement of the push button away from, and tends to return it to its off position, is varied. This enables the operator to determine when the push button reaches each on position on either direction of push button movement, and assists the operator in maintaining the push button in any intermediate on position when this is desirable.

The elongation of the contact supports F, F etc., insures a desirably slight but constant spring force action on the contacts. The fact that the latter are free to turn about portions of their supports which are transverse to the line of movement of the push. button means, of course, that the frictional resistance of the contacts to the movement of the push button is the relatively slight resistance due to a rolling contact, as compared with the relatively heavy resistance due to a sliding contact. The fact that the successively engaged contacts E, E etc., are at opposite sides of the push button, reduces the maximum resultant lateral thrust on the push button, to that of a single contact and its spring support. The shape and character of the thimble b and contacts E, E etc., reduces the damage from spark-- ing between the thimble and contacts to a practical minimum. If and when the contact surfaces accumulate dirt, those surfaces may be subjected to an efiective cleaning action without dismantling the switch mechanism, by rotating the push button and thus rubbing the thimble against the contacts and the surrounding wall of the chamber A With the construction described, each push button unit is a completely operative switch structure which could be removed from the casing M and separately used without modification other than the addition of means to removably secure the block D in place in the body A, although, of course, some casing to enclose the terminal connections would ordinarily be desirable. The formation of the different push button switches as separate units obviously facilitates their assemblage in casings shaped to hold the particular number of push button switches required for my articular installation.

As those skilled in the art will readily understand, my improved master switch mechanism rnay be utilized in motor control circuits of varying forms. In Fig. 6, by way of example, I have illustrated one use of two of my improved push button units in operating a reversible motor 0 at variable speeds in each direction. In Fig. 6 the upper of the two push button switches shown, controls the energization of the motor in one direction, which for convenience I refer to as the forward direction, and the lower push button switch controls the operation of the motor in the opposite or reverse direction.

In Fig. 6, L and L represent the supply conductors, the field of the motor 0 being connected permanently in the supply conductor L. In the inoperative or non-running condition of the motor, the motor armature terminals 7 and 8 are not connected to either supply conductor. When the upper or forward push button switch is actuated sufiiciently to seat the contact E in the groove b" of its thimble b, so that the latter connects the contacts E and E of the switch, a circuit connection between the supply conductors L and L is completed. That circuit connection comprises the conductor I, contact E and contact E of the forward push button switch, the winding Q of an electro-magnetic switch or reversing contactor, and a conductor 9. The energization of the winding Q moves the switch blades Q and Q of the reversing contactor into engagement with stationary contacts connected to the supply conductors L and L respectively. The switch blade Q then connects the supply conductor to the motor armature terminal 8 through motor resistance sections R, R R and R and a conductor l0, while the switch blade Q connects the other motor armature terminal l to the supply conductor L With the circuit connections just described, the motor armature is connected in series with the motor field winding OE and the resistance sections R, R R and R between the supply conductors L and L and the motor is thereby energized for operation in the forward direction at its slowest speed.

When the upper or forward push button switch is thereafter actuated to advance the thimble 2) until it engages the contact E the conductor 3 is thereby connected through the contacts E and E and thimble b to the conductor l and thereby to the supply conductor L. The conductor 3 leads to one terminal of the winding S of an electro-magnetic switch serving as an accelerating contactor. The other terminal of the winding S is connected to the supply conductor L by a conductor II. The energization of the winding S thus produced moves the accelerating contactor switch blade 8 into engagement with a contact connected to the junction point between the motor resistance sections R and R The other terminal of the resistance section R is connected by a short circuiting conductor l2 to he switch blade In consequence, the latter and the conductor [2 short-circuits the resistance R and correspondingly increases the speed of the motor.

The advancement of the upper or forward push button switch into successive engagements with the contacts E E and E successively energizes the windings S S and S, respectively, of other accelerating contactors. When the windings S is energized, the cooperating switch blade 5 is moved to short-circuit the resistance section R and correspondingly increase the motor speed. Similarly, the successive energizations of the windings S and S and the resultant movements of the corresponding switch blades 5 and s successively cut out the resistance sections R and R and correspondingly increase the motor speed. When the upper or forward push button switch is returned to its off position the resistance sections R, R R and R are successively cut back into circuit and finally the reversing relay winding Q is de-energized and the corresponding switch blades Q and Q open and thereby tie-energize the motor.

With the motor in its de-energized position, an actuation of the lower or reverse push button switch such that its thimble 13 connects the contacts E and E of that switch, completes an energizing circuit for the winding QA of a second reversing contactor. That energizing circuit comprises the contacts E and E of the lower or reverse push button switch, a conductor IA connecting said contact E to the previously mentioned conductor l and thereby to the supply conductor L, a conductor 2A connecting the last mentioned contact E to one terminal of the winding QA, and a conductor 9 connecting the other terminal of said winding to supply conductor L The energization of the winding QA connects the corresponding reversing contactor switch blades QA and QA to the supply conductors L and L respectively. The switch QA' is connects to the motor terminal I. The switch blade QA is connected to the motor armature terminal 8 through the resistance sections R, R and R The closure of the switch blades QA and QA thus connects the motor armature and resistance sections R, R R and R in series with the motor field winding OF between the supply conductors L and L but in this case the armature terminals 1 and 8 are connected to the supply conductors L and L respectively, so that the motor will run in the opposite direction from that in which it ran when the actuation of the upper or forward push button switch connected the terminals l' and 8 to the conductors L and L.

The contacts E E E and E of the lower or reverse push button switch are connected by conductors 3A, RA, 5A and 6A, to the previously mentioned conductors 3, 4, 5 and 6, respectively. In consequence, the advancement of the thimble b of the lower or reverse push button switch successively into engagement with the contacts E E, E and E successively cuts out the motor resistance sections R R R and R, and correspondingly increases the speed of the motor in the reverse direction.

I have found that while the contacts in a switch in the push button mechanism disclosed will successfully control the currents required for the operative coils of magnetic switches of 25 amperes capacity or more, it is possible that the inductive currents from the coils of large magnetic switches may cause destructive sparking or arcing at the ball and thimble contacts in the push button switch mechanism. To avoid possibility of such sparking or arcing, I may employ intermediate relay or contactor switches as shown for example in Fig. 7. The arrangement shown in Fig. '7 includes accelerating contactors comprising windings S, S, S and S arranged and controlled exactly as in Fig. 6 but instead of acting directly upon the motor armature circuit those accelerating contactors are employed to control other accelerating contactors including windings SA, SA SA and SA which directly short-circuit the motor circuit resistance sections R, R. R and B. As shown in Fig. 7, the switch members s, 8 etc associated with the windings S, S etc., are connected at their lower ends to the branch from the conductor I which runs to the supply conductor L. Said switch members, when closed, engage corresponding terminals of the windings SA, SA SA and SA". The other terminals of the last mentioned windings are connected to a branch IA from the conductor II running to the supply conductor L The emergency stop, previously mentioned as desirably employed to open the circuit of all the push buttons when conditions require, may advantageously take the form of a simple normally closed push button switch e, which is mounted in the master switch housing M as shown in Fig. 1, and comprises two stationary contacts e and e connected one to one, and the other to the second of two sections of the emergency conductor l as s own in Fig. '7. Normally the contacts e and e are connected by the movable contact 6 but when the push button of the switch 6 is actuated, the contact e is moved to the left from the position shown in Fig. '7, thereby deenergizing each of the difierent contacts E E E While in accordance with the provision of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims and that in some cases certain features my invention may be used to advantage without corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. A push button mechanism adapted for crane and hoist variable speed motor control and comprising a switch body, a longitudinally movable push button actuated plunger mounted in said body for advancement by finger actuation from initial position in successive steps into operatpositions at successively greater distances from said initial position, a return spring opposing such advancement and tending to return said plunger to said initial position, and a plurality of circuit controlling elements mounted in said body for movement into and out of the path of movement of said plunger and each including resilient means opposing movement of the element out of and tending to hold the element in said path, said elements and plunger being so relatively arranged that one or another of said elements is engaged and moved out of, or is permitted to return into said path by said plunger accordingly, as the latter is advanced into or returned from one or another of said different operating positions, the said elements successively engaged and disengaged by said plunger on a continuous movement of the latter in one direction or the other, being located at different sides of the path of movement of the plunger so as to thereby minimize the resultant lateral thrust on the plunger of the different elements engaged by the latter.

2. A push button switch comprising a body of insulating material of rectangular cross sectional outline, and formed with a central chamber and apertures in the wall of said chamber at opposite sides of the chamber and at different points along its length, grooves transverse to the length of said chamber in the opposite outer walls of said body, each intersecting with a corresponding one of said apertures, resilient contact supports, each comprising a bar-like portion located in a corresponding one of said grooves, a rolling contact of circular cross section located in each of said apertures and formed with an axial passage through which the corresponding contact support portion extends, and a contact engaging member movable longitudinally in said chamber and successively engaging said contacts as it is moved in one direction past said apertures.

3. A push button switch consisting of a frame of insulating material, a member slidably mounted thereon, a plurality of rolling contacts disposed on opposite sides of said sliding member in such position that as said member is moved in one direction it alternately engages contacts on the opposite sides of said member and alternately separates from the contacts so engaged on its return movement.

4. A push button switch mechanism adapted for crane and hoist variable speed motor control, and comprising a switch body, a longitudinally movable push button actuated plunger mounted in said body for advancement by finger actuation from an initial position in successive steps, a return spring opposing such advancement and tending to return said plunger to said initial position, and a plurality of spring contact men bers mounted in said body and each comprising a rolling plunger engaging contact and a support therefor having one end anchored to said body and having a portion at its opposite end forming an axle for said rolling contact extending transversely to the path of movement or" said plunger, and having an elongated intermediate resilient portion substantially at right angles to said axle and adapted to flex in a plane transverse to said axle and resiliently holding the corresponding rolling contact in engagement with said plunger when the latter is advanced along its path to permit such engagement, said rolling contacts being distributed longitudinally of said path.

5. A push button switch mechanism adapted for crane and hoist variable speed motor control, and comprising a switch body, a longitudinally movable push button actuated plunger mounted in said body for advancement by finger actuation from an initial position in successive steps,

a return spring opposing such advancement and tending to return said plunger to said initial position, a plurality of spring contact members mounted in said body and each comprising a rolling plunger engaging contact and a support therefor external to and having one end anchored to said body and having a portion at its opposite end forming an axle for said rolling contact extending transversely to the path of movement of said plunger and having an elongated intermediate resilient portion substantially at right angles to said axle and adapted to flex in a plane transverse to said axle and resiliently holding the corresponding rolling contact in engagement with said plunger when the latter is advanced along its path to permit such engagement, said rolling contacts being distributed longitudinally of said path, and said body being formed with openings to permit engagement of said rolling contacts with said plunger.

6. A push button switch mechanism adapted for crane and hoist Variable speed motor control, and comprising a switch body, a longitudinally movable push button actuated plunger mounted in said body for advancement by finger actuation from an initial position in successive steps, a return spring opposing such advancement and tending to return said plunger to said initial position, a plurality of spring contact me nbers mounted in said body and each comprising a rolling plunger engaging contact and a support therefor external to and having one end anchored to said body and having a portion at its opposite end providing an axle support for said rolling portion extending transversely to the path of movement of said plunger and having an elongated intermediate resilient portion substantially at right angles to said axle and adapted to flex in a plane transverse to said axle and resiliently holding the corresponding rolling contact in engagement with said plunger when the latter is advanced along its path to permit such engagement, said rolling contacts being distributed longitudinally of said path, and said body being formed with openings to permit movements of said rolling contacts radially into and out of positions in which they extend into the path of movement of said plunger, and said body being provided with surfaces engaged by said supports and limiting the radial inward movement of said rolling contacts.

7. A push button switch, comprising a body of insulating material of rectangular cross sectional outline and formed with a central chamber and with apertures in the wall of said chamber at opposite sides of the chamber, and at diilerent points along its length, separate contacts received in the different apertures, a separate resilient contact support for each contact, each of said supports including a contact engaging portion at the same side of the chamber as the contact engaged, and another portion on a side of the chamber transverse to the last mentioned side, a terminal connector for each support engaging the last mentioned portion of the latter, the last mentioned portions of said supports being so disposed relative to one another and to the contacts engaged, that the spacing of the different contacts is closer than the spacing of the different terminal connectors in the longitudinal direction of said chamber, and a contact engaging member movable longitudinally in said chamber and successively engaging said contacts as it is moved in one direction past said apertures.

JAMES A. SHEPARD. 

